Filip Rembia*kowski<plk(dot)zuber(at)gmail(dot)com> wrote:
> 2011/1/19 Charles.Hou <givemeegn(at)gmail(dot)com>:
>> " select * from mybook" SQL command also increase the XID ?
>
> Yes. Single SELECT is a transaction. Hence, it needs a transaction
> ID.
No, not in recent versions of PostgreSQL. There's virtual
transaction ID, too; which is all that's needed unless the
transaction writes something.
Also, as a fine point, if you use explicit database transactions
(with BEGIN or START TRANSACTION) then you normally get one XID for
the entire transaction, unless you use SAVEPOINTs.
-Kevin